According to Ars Technica browser user agent strings appearing as iPads running iOS 6.0 have started showing up in their server logs.

[W]e began looking at iPad user agents coming from Apple's corporate IP block in Cupertino and discovered that Apple appears to be surfing the Web using iPads running what looks like iOS 6.0. The whole listing shows iPads running iOS 5, iOS 5.0.1 (the current public release), iOS 5.1 (the upcoming release currently available to developers), and iOS 6. The iPads that appear to be running iOS 6 are also using a slightly newer build of WebKit—the older OSes all show WebKit 534.46, while the ones claiming to be iOS 6 show WebKit build 535.8.

Filtering out IP addresses originating from Apple’s corporate facilities greatly reduces the likelihood of faked strings, but then again Apple is known for their disinformation campaigns. A separate Ars' claim link visits by devices with a resolution of 2048x1536 to the next generation iPad are less sound. As MacRumors points out these devices wouldn’t register on Google Analytics as supporting a 2048x1536 resolution as web content would be far too small to be useful on the device. Rather, like the retina displays on the iPhone 4/4S the next generation iPad would report it’s resolution at the lower 1024x768 to browsers and use the higher pixel density to increase sharpness instead of screen real estate.

As I already mentioned on the iDownloadBlog post of this, it's probably fake, there's no Mobile or Safari identifiers in the user agent.
Also, Ars should track window.devicePixelRatio in javascript so if Apple comes back, they know if it's retina or not.

I imagine there likely will be. Each update of iOS will likely introduce more exploits and apple cannot hope to find them all, hence the incremental updates as security flaws are found and patched. It just takes someone smart enough (ie the dev teams) to find and use these exploits and hopefully eventually lead to a jailbreak. Look at the 4s and ipad2 using absinthe.